Capacitor powder

ABSTRACT

Powder for making electric capacitor or the like comprising a ternary niobium-zirconium-titanium alloy. The alloy is selected as to composition and treated to produce and retain the beta (body-centered-cubic) phase. The resultant product affords high capacitor stability and low leakage approaching the characteristics of the more expensive tantalum at a capacitance cost comparable to or better than that of niobium.

Unlted States Patent 91 1 1 ,849,124 Villani ]*Nv. 19, 1974 CAPACITORPOWDER 2,985,531 5/1961 Gordon et a1 75/177 x 3,038,798 6 1962 B t l 75177 X [75] Inventor: Gerard Needham Mass- 3,203,793 811965 112?; 75/174[73] Assigneez Norton Company Worcester Mass 3,408,604 10/1968 15616111. 75 177 x 3,515,545 6/1970 Canomco et al 75/177 X Notice: Theportion of the term of this patent subsequent to Aug. 10, 1988, OTHER UCATIO S has been dlsclalmed' Fiz. Metal Metalloved 23, No. 1., pages28-36, 1967. [22] Filed: July 26, 1971 [21] App], No,; 166,220 PrimaryExaminer-Charles N. Lovell Related U S Application Data Attorney, Agent,or FirmOliver W. Hayes [63] Continuation-impart of Ser. No. 882,482,Dec. 5,

1969, Pat. No. 3,597,664. [57] ABSTRACT [52] Cl 75/177 75/0 5 BB 75/134N Powder for making electric capacitor or the like com- 2 75/175 prisinga ternary niobium-zirc onium-titanium alloy. [51] hm Cl 6 /0. The alloyis selected as to composition and treated to [58] Field 5 R 134 Nproduce and retain the beta (body-centered-cubic) 5 3 phase. Theresultant product affords high capacitor stability and low leakageapproaching the characteris- [56] References Cited tics of the moreexpensive tantalum at a capacitance cost comparable to or better thanthat of niobium. UNITED STATES PATENTS 2,107,279 2/1938 Balke et a1 /O.5BB 6 Claims, 13 Drawing Figures PATENTEL 1 9974' 3. 849.124

sum 2 or s PATENTEL 53V 1 3,849,124

SHEET 30F 5 Fig.7

40 v 171: V v

ZIRCONIUM ZIRCONIUM F, TERNAF1Y COMPOSITION DIAGRAM L (ATOMIC PERCENT)INWTN'H )RS ATTORNEYS PATENTE 2:24 1 s 1914 SHEET u 0F 5 PAIENIE; as": 191974 SHEET 5 BF 5 CAPACITOR POWDER This application is acontinuation-in-part of U.S. application, Ser. No. 882,482, filed Dec.5, 1969 now U.S. Pat. No. 3,597,664 issued Aug. 3, 1971.

This invention relates to electric capacitors, particularly electrolyticcapacitors and materials used in mak* ing them.

BACKGROUND High performance capacitors are utilized in a wide variety ofradio, television, computer, telephone and other electric circuits. Theprincipal high performance material in the present state of the art istantalum. It is a high temperature, highly corrosion resistant metalcapable of forming a highly stable oxide film, of high dielectricconstant, at its surface which serves as the capacitor dielectric.

With the current increased demand for tantalum and relative scarcity ofworld sources for tantalum ore, the need for a substitute has been ofgreat importance to users of high performance capacitors. The moreabundant, less expensive, metal aluminum is a possible substitute. Butit cannot be formed into porous slug type of capacitors as readily astantalum. Furthermore, aluminum oxide has low dielectric constant givingabout one-third the capacitance of tantalum on an equivalent volumebasis. Another obvious candidate as a tantalum substitute is niobium.Niobium oxide has a higher dielectric constant than tantalum and niobiummetal can be produced at less cost. Niobium powders can also be utilizedto produce porous slugs for electrolytic wet and dry capacitors. TheU.S. Government and leading capacitor and materials manufacturers havetherefore devoted intense research effort to niobium and its alloys (andalso to titanium and zirconium alloys) to'provide a tantalum substitute.The results of these efforts are reported in articles or reports locatedat:

a. Journal of the Electrochemical Society: vol. 108, pp. 343, 750,1,023; vol. 100, p. 69; vol. 110, p. 1,277; vol. 111, p. 1,331; vol.113, pp. 100,1,048 (see also vol. 114, p. 145) b. Journal ofElectrochemical Technology: vol. 1, p.

93; vol. 2

c. Government Contract cl. U.S. Pat. Nos. 3,126,503; 3,278,344;3,321,677

(niobium-zirconium-titanium alloys) 3,203,793

e. Canadian Pat. No. 709,982

None of the work has produced a tantalum substitute which is in wide useat the present time although some of the resultant products were incommercial use for a time.

It has been apparent from the above published work that wet and solidelectrolytic niobium capacitors are not as good as tantalum electrolyticcapacitors in re; spect of leakage, capacitance and dissipationstability, especially at elevated temperatures.

Niobium can nevertheless be used for low capacitance-voltage ratings andalloyed with tantalum for use at higher capacitance-voltage ratings butcannot provide the desired substitute for tantalum for' substantiallyall purposes, including cost.

Reports: AD6 1 805 5,

OBJECT It is the object of the present invention to solve the problem ofproviding a substitute capacitor material satisfying the purposes of thesubstantially unsuccessful development campaign of the prior art.

GENERAL DESCRIPTION down voltages of niobium (in the absence of grossimpurities) are a result of damage inflicted by locally hightemperatures and currents, it would be necessary to reduce these andthis is possible through alloying niobium with a metal which forms amore refractory oxide. Youngs book, Anodic Oxide Films (Academic Press,1961 indicates an inverse relationship between dielectric constant andionic conduction of anodic oxide films. A condition for alloying agentcandidates is that the alloying agent must have a solid solubility inniobium which is true of the Group IVB, VB, VIB refractory metals.Zirconium gives the optimum balance of cost, stability of oxide,solubility. An alloy of Niobium 50 atomic percent zirconium whenfabricated to a sheet form anode and incorporated in a capacitor(anodized in 0.01 percent phosphoric acid to 200 volts at 25C) has goodleakage and exhibits a change in capacitance on heating to 300C in airfor 30 minutes of less than 10 percent, whereas a niobium capacitorchanges by percent.

However,'it was discovered that when porous anodes are made from apowder form alloy of niobium-5O zirconium, they will not anodize above100 volts and that they exhibit high leakage. Difficulty was alsoencountered in anodizing in that the alloy did not anodize well inaqueous electrolytes and organic electrolytes were too viscous for usein a porous structure.

Photomicrographs of Nb-50 AT. Zr anodes revealed a two phasemetallurgical structure of Zr and Nb rich compositions within the porousanode, apparently resulting from the high oxygen contents and highsurface area inherently obtained in powdered materials both of whichtend to promote instability of a single phase, high temperaturestructure. It was then conceived to stabilize the beta phase as a newapproach to the problem and utilize a third alloy addition for thispurpose.

Titanium was chosen because it forms a larger solid solution range withniobium than does zirconium and also lowers the beta and alphatransitions of niobiumzirconium so that the high temperature beta phasecould be retained by rapid cooling to lower temperatures. Titanium wasalso intended to render the overall alloy more readily anodized inaqueous solutions.

It has been found, surprisingly, that the best alloys for porouscapacitor anode purposes are formed when the niobium and titanium arepresent in the alloy in substantially equal atomic amounts, and with agreater portion of zirconium than niobium or titanium. It is alsonecessary to avoid the titanium-rich and zirconium-rich portions of theternary alloy system. Some niobiumzirconium rich portions of the ternaryalloy must also be avoided. For these reasons, it is important tomaintain a single, crystalline structure of controllable composition.

Some care in material processing, as described below, is a necessaryadjunct to material selection in order to achieve the beta, single phasecrystalline structure in the product.

Other objects, features and advantages will in part be obvious from thisdisclosure and will in part be set forth hereinafter in this disclosurein the following specific description which is set forth with referenceto the accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWING FIGS. 1-5 are microphotographs ofsectioned anodes made of compositions and including, by contrast, FIGS.lA-lC showing anodes of other compositions,

FIGS. 6-7 are schematic cross-section views of capacitors utilizing theinvention, and

FIG. 8 is a ternary phase diagram of the niobium-zirconium-titaniumsystem showing data points used in the examples.

FIG. 9 represents the DC leakage over the entire ternary phase diagram,and FIG. 10 represents the thermal stability of capacitance over theentire ternary e qtia raim DETAILED DESCRIPTION OF PREFERRED EMBODIMENTSSince the anodic film is formed from the alloy, the

.films properties are dependent upon the alloy composition. Alloys richin niobium, titanium, or zirconium do not form coherent or thermallystable anodic films. Alloys containing to 60% Nb, Zr, or Ti are better,but they tend to decompose into two or three crystalline forms with anaccompanying change in chemical composition towards the niobium,zirconium, and titanium rich portion of the ternary system, withresulting poor anodic film properties. For these reasons, it isimportant that the alloy remain as a single, crystalline structure ofconstant composition, preferably a single solid solution, beta (bodycentered cubic) phase. Complete beta phase, solid solution only occursat temperatures above about 1,000C. It is therefore necessary tohomogenize this alloy above this temperature and cool it with sufficientrapidity to retain the high temperature, beta phase structure. Somecompositions, notably the Nb-Zr rich regions, are highly unstable andrapidlyform second phases on cooling, The addition of titanium not onlylowers the phase transition temperature but extends the solid solubilityrange and readily promotes the retention of the high temperature betaphase during cooling.

It can be seen from the tables in the Examples below that most of thealloy compositions can produce 200- volt anodic films, useful ascapacitor devices. preferred alloy compositions are characterized by lowleakage and a low capacitance change (AC) on thermal treatment. Thesealloys would be useful for elevated temperature use. They normallycontain 20-40% Nb, -60% Zr, and 20-40% Ti.

Best results occur when the niobium and titanium are in substantiallyequal atomic concentrations (within 10 percent of the total).

From life test data of porous anode, solid electrolyte capacitors inTable 5, it is obvious that essentially all of the compositions andessentially the whole system (i.e., 20-80% Nb, 20-80% Zr, 20-80% Ti) arecapable of being fabricated into useful capacitors. However, somecompositions, namely those stated above, give low leakage and goodstability and are to be preferred over the others.

FIG. Composition (Nb-Zr-Ti) Starting Powder Size 2 30 40 30 325 mesh 5microns 3 30 40 30 60 mesh 325 mesh 4 20 60 20 325 mesh 5 microns 5 2O60 20 60 mesh 325 mesh All magnifications are times in FIGS. 2-5.

The niobium-zirconium-titanium alloys shown in FIGS. l-S have no secondphase. A precipitated second phase is quite apparent in FIGS. 1A, 1B,1C. In general, a deleterious second phase, if produced, will be visibleat 100 times optical magnification and can be regarded as undesired ifobserved at as low as 100 times magnification.

The production of the requisite single phase crystalline structure canbe accomplished (a) in-situ in the electrode (during capacitorproduction or prior to capacitor production) or (b) in the production ofstarting materials to be used later in electrode production. In eithercase what is involved is raising the alloy composition material to ahigh enough temperature as in sintering powder or annealing sheet toproduce, as a homogenous solid solution, the single Beta phase hightemperature modification of the alloy structure and to bring it toequilibrium, then cooling with sufficient rapidity to maintain the Betastructure essentially free of any second phase observable at 800 timesmagnification.

A typical cooling schedule for purposes of the invention would be from1,300 to 300C in 20 minutes and could be achieved by continuous movementof parts from a furnace to a cooling zone, as by a conveyor belt.

FIGS. 6-7 show two examples of capacitors utilizing the presentinvention. Each of the capacitors comprises an anode 10 with adielectric comprising at least in part a dielectric oxide film on thesurface of the anode material. The capacitors also comprise a cathodeelectrode 20. Leads 12, 22 are attached to anode l0 and cathode 22respectively. In FIG. 6, the anode has the form of a sintered powderslug and the capacitor is of the electrolytic type with wet or solidelectrolyte 21 impregnating the anode and extending to the cathode. FIG.6 also shows conventional capacitor packaging elements as a seal 30 andplastic encapsulant 32. The anode 10 in the FIG. 7 capacitor is a rolledfoil or a film sputtered from a sputtering target and includes adielectric oxide film 11 on the anode surface.

The invention can also be utilized in non-polar capacitors, as well asthe polar capacitors of FIGS. 6-7, and in other electrical, chemical andelectrochemical devices requiring the significant characteristics of atantalum substitute material as described herein.

FIG. 8 is a ternary diagram showing the various data points refereed toin the examples below. The percentages on the three sides of the diagramare atomic percentages.

The compositions indicated are based on proportions of startingmaterials used. At any given location in a powder or other productproduced from the starting materials by melting together, thecomposition may vary due to the known metallurgical phenomenon of 5coring as the melt is cooled. Generally, the compositional differencesfound along the material on a microscopic scale are acceptable. Howeverit is preferable to minimize compositional variation due to coringduring ingot solidification and this can be accomplished byhomogenization heat treatment applied either as an additional stepimmediately after melting and cooling the alloy and/or in the course ofthe fabrication steps (e.g., sintering powder or annealing foil), asnoted above.

It is preferred and distinctly advantageous to select alloy compositionsof substantially of atomic proportions:

niobium 2.040% zirconium 30-60% titanium -40'7r with equal atomicproportions of niobium and titanium, particularly where (l) fine powders(6 microns Fisher Average Particle Diameter F.A.P.D. or less) areproduced, (2) where high oxygen impurity levels are in the material, (30where hydrogen addition processing is used as an aid to pulverizing.

An alloy composition of essentially (within plus or minus 5 percent) thefollowing atomic proportions:

50% zirconium niobium 25% titanium (data point 9 in FIG. 8) has beenfound to be distinctly advantageous for fine powder production andretain a single beta phase composition under processing conditions whichproduced multiphase crystal structure in powder of alloy compositioncorresponding to data points 15 and 16 and was fabricated into solidelectrolytic capacitors along with (and under identical conditions with)powderof alloy compositions 6 and 16 and produced superior capacitorswith respect thereto in terms of affording an economic tantalumcapacitor substitute.

While any of several methods of alloy powder production are feasible(including co-reduction of their mixed halides) it is preferred anddistinctly advantageous to obtain the three alloy components Nb, Zr, Tiin elemental form, melt them together and cool to form an alloy ingot,hydride the ingot to embrittle it, pulverize the hydrided ingot anddehydride the powder so formed by heating.

The dehydriding can be done on the powder, per se, or in conjunctionwith sintering the powder to an anode compact, the former beingpreferred.

Melting, hydriding, pulverizing and dehydriding tends to produce ahighly agglomerated alloy powder, which is advantageous for compactingand tends to retain high capacitance consistent with low leakageproduced by cleansing impurities in the various melting, heating and gaspurging steps. The agglomerated particles contain individual fine powderparticles in the range of 18 microns or less with the agglomerates perse being plus 325 mesh, minus mesh.

The practice and relative value of the invention is illustrated by thefollowing non-limiting examples (including some specimens outside theinvention scope):

EXAMPLE 1 Several alloys of nominal compositions listed in Tables l-'3below were made by are melting.50-.l00 gram alloy buttons in argonatmosphere using a nonconsumable tungsten electrode. The buttoms wereformed from niobium chips and crystal bar zirconium and titanium withraw material specification as in Example 2 (below). Each alloy buttonwas melted four times and then heated to about percent of the meltingpoint and held at that temperature for 2 hours. The buttons were thensliced with a diamond wheel saw. One slice of each button was chemicallyanalyzed and the remainder were cold rolled from three-sixteenths inchto a thickness of about 0.015 inch. The rolled sheets were cut intopanels, degreased, chemically polished, rinsed and annealed above 1,000Cat about 80 percent of their respective melting points for 30 minutes ina vacuum of about 10 torr. The panels were anodized at 1 ma cm ofsurface: in 0.01% H PO (at 25C in one test and at 92C in a second test)to 200 volts and held for 30 minutes. The anodized panels were rinsedand dried and electrically tested in a wet cell (1% Fl PO electrolyte)as formed and again after a later heat treatment of 300C for 30 minutesin air.

'of a strained body-centered-cubic phase quenched from a hightemperature. There was no evidence of second phase transformation exceptin data points 19 and 21; these had fine precipitated structures withinthe equiaxed structure.

The data points in Tables 1-2 are grouped from lowest leakage to highestleakage. Table 3 shows a further series of experimental resultsindicating reproducibility of the Table 2 data.

TABLE ICn1inued DATA NOMINAL Cap.

COMPOSITION POINT Nb-Zr-Ti (At. DCL DF muf/Cm A C% Niobium .06 2.5 78 72TantuIum .02 2.1 68 3.0

TABLE II DATA NOMINAL Cap. A C

COMPOSITION POINT Nb-Zr-Ti (At. DCL DF muf/cm 17 30-10-60 2.1 2.2 47 9111 30-60-10 7.4 4.4 7 20-40-40 9.5 7.5 3 60-30-10 22 5.0 14 20-20-60 3711.2 23 10-25-65 High 5.7 8 -50-15 High 10 20 10-40-50 High 13 Tantalum.02 1.6 54 2.2

Niobium High (will not anodize) TABLE III DATA NOMINAL Cap.

COMPOSITION POINT Nb-Zr-Ti (At. DCL DF muf/cm A C TABLE 111 ContinuedDATA NOMINAL Cap.

cOMPosmON POINT Nb-Zr-Ti (At. DCL DF muf/cm A C EXAMPLE 2 age for 2hours. As a control, niobium anodes were sim- Several alloy buttons wereformed by melting together niobium, zirconium and titanium with thefollowing purities:

(machining chips) (crystal bar) (crystal bar) The nominal compositionsof the alloys are given in Table 4. The buttons were hydrided, ground topowder and dehydrided. The powders in varying size cuts were sinteredabove 1,000C into porous compacts of approximately 1 gram each, cooledand anodized in 0.01% H PO electrolyte at 92C temperature with a currentdensity of 63 ma per anode to a formation voltto break-down. Thereformation break-down is given in Table 4 as V Similar capacitorsamples were reformed to 35 volts.

tested at 20 volts for capacitance and leakage. The results are given inTable 4.

TABLE 4 NOMINAL ATOMIC *POWDER L/C DATA COMPOSITION SIZE/SINTER V CAP.[1, amp. POINT (Nb-Zr-Ti) TEMP (C] (VOLTS) (pfd) pfd.

2-1 33-33-33 F/1100 23.3 .39 2-2 33-33-33 F/lZOO 40 16.5 .07 2-333-33-33 1 /1300 40 12.4 .51 2-4 33-33-33 C/1300 40 5.3 .26 5 40-40-40F/1300 65 1 1.7 .22 6-1 30-40-30 F/1100 47 12.0 .17 6-2 30-40-30 C/120047 5.4 2.3 6-3 30-40-30 C/1300 52 4.8 .35 6-4 30-40-30 C/1100 18.0 .089-1 25-50-25 F/l200 40 8.6 .14 9-2 25-50-25 F/1200 63 8.9 .06 9-325-50-25 C/1300 38 4.4 .11 9-4 25-50-25 C/1300 65 4.4 .05 12-1 20-60-20F/1100 80 7.8 .06 12-2 20-60-20 C/1200 62 4.5 .13 .12-3 20-60-20 C/l30062 4.5 .13 13 15-50-25 F/1100 63 14.2 .09 15-1 40-20-40 F/1100 55 11.22.0 15-2 40-20-40 C/1200 58 9.9 1.6 15-3 40-20-40 C/1300 42 4.7 2.5 16-160-20-20 F/1300 56 I 15.4 16-2 60-20-20 C/1400 58 5.8 1.1 22 10-60-30F/1100 13.1 .31 24 25-25-50 F/1200 67 11.5 .65 CONTROL 100-0-0 A/205015.3 .10

F cut is -325 mesh +5 micron, C cut is mesh 325 mesh. A cut is l40 mesh+5 microns F.A.P.D.

25C Test for 100-04), 851or others A counter-electrode was added and thedevices were life tests of 200 to 1,000 hours and resultant life testdata 15 charted in Table 5. In the life tests, leakage cur- The lifetesting acted as a burn-in for capacitors. tending to stabilize them,for better performance in future life testing and would be a desirablestep for capacitor production.

rents capacitance and dissipation factor are measured TABLE 6 A at 25C.Then thetemperature is raised to 85C and the capacitors retested.Temperature is held at 85C for an ANODE PRO ESSI extended period, thecapacitors retested and then the G t 1'88" 111 C1 temperature is droppedto 25C for retest. ln1t1al (I) Weight (gm) Density (glee) U Time andfinal (F) values of these parameters are shown in Table 5. In someinstances the final value at high 5 temperature is a median or averagevalue. 16 I 31 4 L10 ,3 hr:

TABLE 5 Initial and final median or average values at 25 C. and 92 C.

Nominal composition Leakage (microamps) Capacitance 1) Dissipationfactor, percent At. percent Data point I 85 F35 F 25 25 35 F35 F25 125135 F35 F25 2 33. 3-33.3-33. 3 0.3 -37 15.5 21.0 13.0 17.0 10.3 14.515.9 5-..- 40-40- 2.0 13 11.7 13.1 12.5 7.2 4.3 7.5 2.3 0 (30-1030 1.710 15.0 17.5 15.0 12.2 10.7 10.2 5.3 0.- 25-50-25 0.0 3.0 3.3 10.1 0.07.3 5.3 7.2 3.3 12 -00-20) 0.5 3.5 7.3 3.7 3.2 4.0 7.3 0.0 13 15-50-25)1.2 7.2 14.2 15.7 14.4 10.3 9.2 15 4020-40 10.0 55 10.5 15.0 11.4 21.021.0 15.5 10- 00-20-20) 04 2.2 15.4 10.3 17.3 22.0 13.0 13.3 22- 1000-304.1 24 13.1 15.3 10.0 3.0 5.3 3.4 24 (25-25-50 7.5 23 11.5 13.4 12.417.0 3.1 12.1 Niobium (1.5. 1000-0) 1.0 2.4 15.3 17.5 15.0 15.0 10.025.0

e 1 of 9 samples tested at data point 2 was a failure (i.e. Leakage inrising to the milliampere range). 1 failure out of 4 samples tested atdata point 15. a 2 failures out of 3 samples tested at data po nt 16. My

EXAMPLE 3 FORMATION Solid electrolytic capacitors were prepared as inExample 2 using the alloy compositions identified as 6, l2 o and 16 inTable 5. Specific anode sintering and dielec- Electrolyte 3 Hspo at 92Current Density: 63 ma/anode. tr1c oxide formation conditions are givenin Table 6A.

These ca acitors were tested for electrical ro erties Formation Voltage:200 Volts P P p 0 Hold Time at Voltage: 2 Hours. at room temperaturesand then life tested at 85 C V v under 20 volts bias for 1,000 hours.The results are given in Table 6B. EXAMPLE 4 The results were inagreement with those tabulated in Table 5 except that composition 16 hadimproved leakage behavior. However, the alloy also exhibited capacityinstability. Y

Solid electrolytic capacitors were prepared using the alloy compositionsidentified as data points 6, 9, l5, 16

TABLE 6B COMPOSITION LIFE TEST TEMP L C L/C DF NUMBER HOURS (C)(ya/anode, med.) (pf/anode. avg.) (pa/11f) (7r) Table 7 PowderPreparation 1. Melt together, to form a solid alloy ingot, Nb, Zr, Tiwith commercial purities shown in Table 7-1(a) to produce an ingot withpurities shown in Table 7-1(b).

2. Hydride ingot by heating in a hydrogen atmosphere at 700C for aboutan hour or until hydrogen pick-up becomes very slow and cool to 600C andrepeat again at 500, 400, 300 and then cool to ambient.

3. Process ingot to powder by crushing to l mesh, then ball milling toproduce powder.

4. Screen powder to final desired size distribution by mechanical orfluid classification technique.

5. Dehydride by heating powder to 700C in a chamber under subatmosphericpressure, coming up to temperature slowly to avoid an excessive rate ofhydrogen evolution which would create an explosion hazard, holding at700C until hydrogen content is reduced to less than 500 parts permillion.

6. Cool and then passivate by slowly admitting air to the powder beforeopening up the chamber.

7. The lightly sintered cake resulting from (4)-(6) is lightly crushedto pass a 60 mesh/inch screen (A.S.T.M.). The resultant product is anagglomerated powder with individual particles in the range of 4-18microns. Some 75 percent of the material are in agglomerate form with asize of between plus 325 mesh and minus 60mesh. The powdered material asa whole has a Fisher Average Particle Diameter of 5-6 microns.

Table 8 Capacitor Preparation 1. Press powder using 8 percent by weightcamphor addition to achieve a green compact of green density (Dg) asshown in Table 8-1.

2. Sinter for 30 minutes to temperatures shown in Table 8-1 to densitiesshown in Table 8-1 producing anodes having the sintered density (Ds) andcarbon im- 10 purity content shown in Table 8-1.

3. Anodize (form) alloy in 0.1% H PO at 92C to 80 volts at 120milliamperes per anode. Similarly anodizc niobium control at 25C.

3a. Perform wet cell testing as shown in Table 8-1,

measuring or calculating from measurements leakage, (in microamperes),leakage to capacitance ratio (microamperes per microfarad), capacitance,specific capacitance by weight and volume (microfarad-volts per gram andcubic centimeter, respectively), dissipation factor and equivalentseries resistance. Alloy powder of data point 15 had very high leakage(in excess of 1 milliamp).

4. Impregnate and pyrolyze by (a) dipping for 3 minutes in 12%concentration of manganese nitrate solution, pyrolyzing for 8 minutes at275C, and repeat this process two more times, then reforming to 35volts; (b) dipping again in 25 percent manganese nitrate for 3 minutes,pyrolyzing for 8 minutes at 275C, and repeat this process two moretimes, then reforming to 35 volts;

(c) dipping again in 50 percent manganese nitrate for not be processedto solid capacitor form, except with great difficulty.

5. Apply counterelectrode (cathode) by coating with colloidal graphite,overcoating with silver paint, attaching a conductor with conductiveepoxy, and encapsu- The powders have the purity shown in Table 7-1(c).4O lating in non-conducting epoxy resin.

TABLE 7-1 Chemical analysis: Starting materials to powder (p.p.m. orwgt. percent) O H N 0 Al. Co Cr 011 Mg Mw M0 Nb Ni Pb Si Sn Ti W Zr(a)Stcarti'.iIi1g ma eras:

Nb barfio ok 80 3 40 20 Zr 1 Table 8-1 Porous Anode and Wei Cell TestData Alloy (Element) 30 min ldenti- Anode Dp Ts Ds Carbon L L/C CV/gCV/cc DF ESR i'icuiion Wt(gni) (g/cc) (Cl (g/cc) m) (pm/12F) C (uf-V/g)(uflV/cc) (71) (Ohms) ppm) NZT (1* 1) .710 3.2 1100 4.4 480 39.0 0.11148. 5.440 1.236 55 15.07 (2) .710 3.2 1050 4.4 610 78.9 1.1 71.7 8.01101.1136 53 9.111

NZT 9* (l) .691 3.0 1000 3.8 164 104.0 1.7 62.1 7,190 1.892 52 11.11 (2).691 3.0 1000 3.7 2200 144.4 2.2 65.6 7,600 2,054 48 9.71 (3) .691 3.01000 3.7 500 129.2 1.7 76.0 8.800 2.378 53 21.60

(Niobium) .920 3.9 1600 5.6 152 9.9 .12 86.0 7,480 1.336 73.5 11.34

(Tantalum) 1.84 8.0 1850 9.1 1.1 0.013 82.5 3,590 395 55 8.85

* 500 Table 7-l Table 9A Life Test Procedures Table 9D Test for leakagecapacitance and dissipation factor D 1 F to DF 7) at C initially. Heatto 85C and retest. Hold at tem- 25 lsslpa ac r 0 perature for about 600hours and then retest. Cool to Test hours 0 01:1. 590 1115. a 25C andretest. Detailed test procedures were in ac- Temp- 25 C 85 C 85 C 25 Ccordance with Example 3 procedures and MILSPEC N216 MIL-C-390o3, (1)14.5 26.5 17.0 15.0 14.0 16.5 The samples were pre-aged at 15 volts biasat 85C 2 0 22 5 through a prior test for 410 hours prior to the testsre- (1) 13.0 23.0 16.0 18.0 ported here. The samples were biased to 20volts for 5:8 532 3:8 :8 these tests using a bias circuit with a seriesresistance NZT-i6 (1) 19.0 31.5 18.5 12.5 of lO-l5 ohms. (2) 2'0 175 8560 Niobium 65.0 51.0 64.0 65.0 Tabb 9B Tantalum 12.0 12.0 12.5 11.5

Leakage (ll- Test Hours 0 hr. 590 hrsv T 25C 85C 85C 25C emp It is seenfrom Table 9B that niobium and alloy com- NzT-6 position NZT-l6increased substantially in leakage in 70 under test conditions, whileNZT-6 and NZT-9 did not (2) 17.0 47.6 94.6 19.5

increase. NZT-9 had the lowest leakage approaching NlZT-9 2 5 l4 0 l0 52 5 tantalum. Table 9C shows fairly stable capacitance and E DF for allsamples tested. Data external to this table (3) 1.5 7.8 10.0 2.0 (e.g.,leakage data) makes clear that the niobium ca- N21) pacitance and DFwould run away upon further life (i) 325 200 432 65,6 testing. There issome likelihood of runaway for I67 343 5O NZT-l6 as well, but thelikelihood is less certain.

Niobium 13.1 76.9 186 144 anta um 0 88 3 7 3 3 0 79 EXAMPLE 5 Table 9CNiobium, zirconium, titanium alloy powders of compositions correspondingto data points 2, 5, 6, 9, 12, 13, Capacitance (pf) 15, 16, 22, 24 ofFIG. 8 were prepared and sintered as anodes. T Test Hours 0 hr 590 hm hl hgsepowders were in a size rangeof 325 Temp mes p us microns(nominally 10 microns Fisher Ayerage Particle Diameter). X-raydiffraction analysis i( 1 Z)T-6 34 0 44 O 39 0 31 6 was made of thepowders per se, and also of samples (2) 5(10 62,0 56,0 410 made bycrushing the anodes, to detect crystal struc- NZT-9 ture (includinglattice parameter) of the phases present (1) 36.1 46.0 42.0 35.0 (2) 460410 310 in the material. The results are shown in Table 10A. (3L1r I38.1 61.1 456 36.0 The procedure was repeated for fine powders (nomi- 6I) 830 I020 940 80.0 nally 4 microns F.A.P.D.) with varying levels ofoxygen 2) 56.0 53.0 58.0 52.0 contamination and the resultant data areshown in Niobium I 83.4 89.0 86.1 72.0 Tantalum 88.0 94.0 940 870 Table108. Table 10B also shows sintermg tempera Table A Crystalline Structure(and Lattice Parameter) Annealed Powder Sintered Anode Data Com ositionMajor Second M3101 Second Point At.% b-Zr-Ti Phase Phase Phase Phase 233.3-33.3 33.3 BCC(3.39) none BCC(3.40) none 5 40 40 BCC(3.49) BCC(3.32)BCC(3,42) none 6 30 40 -30 BCC(3.42) none BCC( 3 .48) none 9 -50 -25BCC(3.4S) none I2 20 60 20 BCC(3.47) none BCCUAZ) none l3 l5 -50 35BCC(3.46) none 15 40 20 40 BCC(3.35) none BCC(3.36) none I6 60 -20 20BCC(3.35) none 22 10 60 BCC(3.48) HCP BCC(3.48) none 24 25 25 -50BCC(3.37) none BCC(3.38) none Table 108 X-Ray Analysis of Nominal 4Micron F.A.P.D. Nb-Zr-Ti Alloys: Crystalline Structure (and LatticeParameter(s)) Data Oxygen- Sinter Sintered Anode Point (Sample) ppmTemp.-C Major Phase Second Phase 6 8800 1100 BCC(Ao:3.4 1) none* 9 (1)ca. 6000 I000 BCC(3.45) none (2) 9400 l 100 BCC(3.45) none* l5 14,4001100 BCC(3.34) BCC(3.45)* 16 (l) ca 6000 1000 BCC(3 34) HCP (A0:

5. l0 (2) 6300 1100 BCC(3.33) HCP (A0:

3.21, Co: 5. l2)

excepting contaminants, such as zirconium oxynitride and oxycarhide.

BCC: body centered cubic (Ao reported) HCP: hexagonal close packed (A0,C0 reported) Although the 10 micron size powders of alloys (data 35(data point) 15 with high oxygen content and slow cooling in Table 108had a double beta (bodycentered-cubic) phase in anode form. Data point16 also had a second phase an HCP structure.

EXAMPLE 6 An extensive number of Nb-Zr-Ti alloy compositions wereprepared by sputtering thin films onto glass slides, anodizing the metalfilm to 200 volts, testing heating to 300C for one-half hour and testingagain in the same manner as Example 1. The results are shown in FIG. 9which represents the DC leakage and FIG. 10 which shows the thermalstability of capacitance over the en tire ternary phase diagram.

The results show that good anodic film properties 10 y.a/cm at 140 V DC)extend over a wide range of compositions beginning in the central regionof the Nb-Zr binary, through the central region of the-Nb-Zr- Ti ternaryand extending toward the central region of the Zr-Ti binary. The regionof high thermal stability of capacitance is more localized near thecenter of the Nb-Zr-Ti ternary with a narrow path extending toward thecentral portion of the Zr-Ti binary and another narrow extension towardthe Zr corner of the ternary, representing equal portions of niobium andtitanium with increasing zirconium concentration.

While the results of sputtered film do not represent the cyrstallinestructures found in the bulk alloy such as annealed sheet or powder orsintered porous anodes,

they do show the effects of chemical composition on the electricalproperties of alloy anodic films. For example, while the centralportions of the ternary and the Nb-Zr and Nb-Ti binaries displayedgoodDC leakage, the same composition cannot be retained in bulk form becauseof phase separation accompanied by compositional changes, unless anextremely rapid quench of the high temperature modification of thesingle BCC structure is used. Retention of the single BCC structure ismore easily accomplished in the bulk when the alloy composition isremoved from the, Nb-Zr and Zr-Ti binary lines by about 10 atomicpercent. The trends shown by data afford approximations of what willoccur in bulk form.

While the present invention has been described with reference to theparticular embodiments thereof, it will be understood from the abovedisclosure by those skilled in the art that numerous modifications maybe made without actually departing from the scope of the invention. Forinstance, the invention contemplates the ternary Nb-Zr-Ti alloy presentalone or as part of a larger alloy (or mixture) system of film-formingmetals. Where the niobium is substituted in any amount by tantalumand/or zirconium and/or titanium is substituted in any amount by hafniumwhere these substitutions are chemically similar to the components ofthe Nb-Zr-Ti ternary. Less similar elements, such as vanadium,molybdenum and tungsten, may be added up to 20 atomic percent of thetotal system without severe degradation. Dissimilar elements, such asiron, chromium and nickel, may be tolerated by as much as 1-5 percent.More dissimilar elements, such as noble metals, alkali, and alkalinemetals, etc., may be considered as true impurities and should be lessthan 1 percent.

In its broadest aspects, the invention comprises aniobium-zirconium-titanium ternary alloy of powder form suitable formaking capacitor anode or the like with the characteristic that it iscapable of forming or retaining an essentially homogeneous crystalstructure of a single phase although it is preferred and distinctlyadvantageous that:

a. the single phase should be a beta (body-centeredcubic) phase, whichis more practicably attainable consistent with capacitor powderpreparation conditions, andlgr M, V .7.

b. that the powder, per se, shall have single phase structure.

The powder is suitable for manufacturing into capacitor anodes whetherin single powder form, agglomerated form, pre-pressed or pre-sinteredpreliminary compact form, or in the form of final sintered anodecompacts which can be re-crushed and remanufactured. Therefore theappended claims are intended to cover all such equivalents or variationsas come within the true spirit of the invention.

1 claim:

1. A powdered material of niobium-zirconiumtitanium ternary alloy, inform suitable for manufacture into an electrolytic capacitor anode, thealloy having an essentially homogeneous crystal structure of a singlebody centered cubic alloy phase wherein the elements of the alloy arepresent in atomic percentages of from:

20 to 40% for niobium 30 to 60% for zirconium 20 to 40% for titanium. 2.The material of claim 1 wherein the niobium and titanium are present inthe alloy in substantially equal atomic amounts.

3. The material of claim 2 having 21 Fisher Average Particle Diameter ofless than 6 microns.

4. The material of claim 3 wherein the elements of the alloy are foundthroughout the material in essentially the atomic proportions of:

50% zirconium 25% niobium 25% titanium.

5. The material of claim 2 wherein the elements of the alloy are foundthroughout the material in essentially the atomic proportions of:

50% zirconium 25% niobium 25% titanium.

6. A capacitor grade powder for use in manufacturing solid electrolyticcapacitor sintered, porous anodes anodizable to,200 volts and affordinghigh thermal stability and low leakage and dissipation factor,consistent with high capacitance, comprising single phasebody-centered-cubic crystal structure niobium-zirconium-titanium ternaryalloy throughout the powder mass, the elements of the alloy beingpresent in essentially homogeneous atomic percentages and within therespective ranges of:

20-80% for niobium,

20-80% for zirconium,

20-80% for titanium, throughout the powder mass.

1. A POWDERED MATERIAL OF NIOBIUM-ZIRCONIUM-TITANIUM TERNARY ALLOY, INFORM SUITABLE FOR MANUFACTURE INTO AN ELECTROLYTIC CAPACITORR ANODE, THEALLOY HAVING AN ESSENTIALLY HOMOGENEOUS CRYSTAL STRUCTURE OF A SINGLEBODY CENTERED CUBIC ALLOY PHASE WHEREIN THE ELEMENTS OF THE ALLOY AREPARESENT IN ATOMIC PERCENTAGES OF FROM: 20 TO 40% FOR NIOBIUM 30 TO 60%FOR ZIRCONIUM 20 TO 40% FOR TITANIUM.
 2. The material of claim 1 whereinthe niobium and titanium are present in the alloy in substantially equalatomic amounts.
 3. The material of claim 2 having a Fisher AverageParticle Diameter of less than 6 microns.
 4. The material of claim 3wherein the elements of the alloy are found throughout the material inessentially the atomic proportions of: 50% zirconium 25% niobium 25%titanium.
 5. The material of claim 2 wHerein the elements of the alloyare found throughout the material in essentially the atomic proportionsof: 50% zirconium 25% niobium 25% titanium.
 6. A capacitor grade powderfor use in manufacturing solid electrolytic capacitor sintered, porousanodes anodizable to 200 volts and affording high thermal stability andlow leakage and dissipation factor, consistent with high capacitance,comprising single phase body-centered-cubic crystal structureniobium-zirconium-titanium ternary alloy throughout the powder mass, theelements of the alloy being present in essentially homogeneous atomicpercentages and within the respective ranges of: 20-80% for niobium,20-80% for zirconium, 20-80% for titanium, throughout the powder mass.